The CAS Registry Mumber 157885-28-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,5,7,8,8 and 5 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 157885-28: (8*1)+(7*5)+(6*7)+(5*8)+(4*8)+(3*5)+(2*2)+(1*8)=184 184 % 10 = 4 So 157885-28-4 is a valid CAS Registry Number.